The subject of the present invention is alcohol-free orthoesters of zirconium and hafnium, and also a method for the preparation of the alcohol-free orthoesters of these metals. The preparation of zirconium and hafnium alkoxides, which are also called zirconic or hafnic acid esters is generally performed like the production of titanic acid esters by the reaction of the corresponding metal halides with alcohoIs. The alcohol that is used serves simultaneously as a solvent for the reaction and for the ester that forms, which is generally used in this solution. The halogen hydride that is released by this reaction is neutralized by the addition of amines.
The resulting products from that procedure contain a considerable polymer content in the form of metal oxane compounds which are produced substantially on the basis of the following secondary reactions.
The alcohol that is put in reacts with the evolving halogen hydride to form alkyl halide and/or alkenes and/or ethers; water is released which in turn has a hydrolyzing action on the metal ester to form metal oxane.
It has furthermore been found that, in the reaction of zirconium or hafnium tetrahalide with excess alcohol, and also in the transesterification of low zirconic or hafnic esters with higher alcohols, a product forms which has a higher molecular weight than corresponds to the formula M(OR).sub.4 (M=Zr or Hf). Studies have shown that this product has one more molecule of the alcohol than corresponds to the formula M(OR)4 (R=alcohol moiety), although this product has also been called a zirconic or hafnic acid ester of the formula M(OR)4 This known product, containing excess alcohol, is in a dimeric or oligomeric form, is a liquid and has been useable heretofore in all applications of zirconic and hafnic acid esters. However, this bound alcohol interferes in special applications, as for example when the known product is used as a catalyst in Ziegler/Natta polymerization reactions.
The object therefore was to prepare alcohol-free esters of zirconic and hafnic acid, and to devise a method for preparing these esters, in which the alcoholic esters would not form and the formation of polymers is lower in comparison to the known methods.